The aims of the research proposed here are to study the structure and function of several membrane proteins in eukaryotic cells: the Band 3 protein of human red blood cells; the (Na+,K+) ATPase of a variety of cells; the Ca++ ATPase of liver plasma membrane; and the Na+/Ca++ exchange protein of cardiac sarcolemma and brain synaptosomes. One aim is to obtain a map showing the arrangement of each polypeptide with respect to the lipid bilayer. Another aim is to study the protein-lipid interactions, the importance of the oligomeric structure, the mechanism of action, and the regulation of these transporters.